1. Field of the Invention
The present invention relates to an apparatus for detecting the contact with a rotating body. More particularly, it relates to an apparatus for detecting the contact between a contact detection member and an outer peripheral surface of a rotating grinding wheel.
2. Discussion of the Prior Art
In a grinding machine, an apparatus for detecting the position of an outer peripheral surface of a rotating grinding wheel prior to truing the grinding surface or grinding a workpiece, uses a contact detection member which is fixed to a head stock on a work table and which incorporates an acoustic emission sensor (AE sensor). A wheel head with a grinding wheel is moved toward the contact detection member and the position of the grinding surface is detected when the grinding surface touches with the contact detection member at which time the AE sensor detects sound wave which is exerted on the detection member. The contact with the grinding wheel is decided based upon the level of a signal output from the AE sensor, and the surface position of the wheel is obtained by reference to the amount of forward feed of the wheel head when the grinding surface is decided as having contacted with the contact detection member.
This apparatus has, however, the following drawback:
For a similar condition to an actual truing or grinding operation, coolant is ejected from a nozzle during such contact detection operation and adversely acts on the contact detection member. The AE sensor detects shocks caused by coolant and outputs an electric signal. As a result, the contact detection apparatus may decide as the contact having been made, in response to the output signal which the AE sensor issues though the grinding surface has actually not touched with the contact detection member.